This application claims the priority to and benefit of Korean Patent Application No. 10-2004-0091522, filed on Nov. 10, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a thin-film transistor (TFT) for a flat panel display. More particularly, the present invention relates to an organic thin-film transistor (OTFT) for preventing damages on the surface of an organic semiconductor layer, a method of fabricating the same, and a flat panel display having the same.
2. Description of the Related Art
An organic thin-film transistor (OTFT) is a drive element for a next generation display that has been actively studied. The OTFT uses an organic material instead of silicon as a semiconductor layer. Depending on the compositional material of the organic layer, there are a low molecular weight OTFTs which are composed of oligothiophene, pentacene, and the like, and a high molecular weight OTFTs which are composed of polythiophenes, and the like.
An organic electroluminescent display device using such an OTFT as a switching element includes at least two OTFTs, for example, one switching OTFT, one drive OTFT, a capacitor, and an organic electroluminescent device which is composed of an organic layer interposed between upper and lower electrodes.
Generally, a flexible organic electroluminescent display device uses a flexible substrate that includes a plastic substrate. As the plastic substrate is very vulnerable to heat, the flexible organic electroluminescent display device must be fabricated using a low temperature process. Since the OTFT using an organic layer as a semiconductor layer can be made through low temperature processes, it is widely used as a switching element for the flexible organic electroluminescent display device.
Korean Patent Publication No. 2004-0028010 discloses a pentacene thin-film transistor for shortening a thin-film deposition time and improving hole mobility. Korean Patent Publication No. 2004-0084427 discloses a structure of an OTFT for improving electrical characteristics of a transistor and a method of forming the same. Further, Japanese Patent Publication No. 2003-92410 discloses a TFT that includes a channel region that is composed of an organic compound having radicals, improves carrier mobility, and an on/off current ratio.
FIG. 1 is a sectional view illustrating a conventional OTFT.
Referring to FIG. 1, the conventional OTFT includes a gate electrode 12 formed on a substrate 11, a gate insulating layer 13 formed on the substrate 11 having the gate electrode 12, source electrode 14 and drain electrode 15 formed on the gate insulating layer 13, and an organic semiconductor layer 16 formed on the source electrode 14, drain electrode 15, and the gate insulating layer 13.
The conventional OTFT structured as above includes an organic semiconductor layer as the semiconductor layer 16. The semiconductor layer 16 is formed on the overall surface of the substrate without patterns. However, as carriers, for example, holes may accumulate between the layers and the organic layer in the conventional OTFT structure, causing an undesired leakage current.
When patterning the semiconductor layer using laser ablation in order to reduce the accumulation of holes, thermal modification at an edge portion 21 of the patterned semiconductor layer 20, as shown in FIG. 2, or a recasting problem may occur.